Development of a sterilizable MRI-compatible manipulator for stereotactic neurosurgery

[Introduction] Almost of all needle insertion manipulator for stereotactic neurosurgery use computed tomography (CT) to scan the brain of the patient before and during operation. Currently, we are developing a needle insertion manipulator for magnetic resonance imaging (MRI)-guided neurosurgery. MRI techniques are getting attractive now for the development of interventional MRI therapies and operations. If an MRI-compatible manipulator is available, these therapies will be minimally invasive, with rich information such as functional imaging, blood flow imaging, and so on. However, actuation of a robot in an MRI environment is difficult because of the presence of strong magnetic fields. Many kinds of manipulators for neurosurgery are already tested clinically and have been proven useful in the operating theatre. However, their clinical application is limited by specific problems including sterilization, the robot’s weight, and safety. [Method] This system frame was manufactured using non-ferromagnetic materials (aluminum) and was actuated using ultrasonic motors (non-ferromagnetic motor). The manipulator has the capacity for cover-sheet-free sterilization. This manipulator has three major components: the main mechanical component (with 6DOF), the torque transmission component, and the electric motor component that cannot be sterilized. The electric parts are detachable. Using this mechanism, we can clearly separate the unsterilizable components from the surgical area. This manipulator achieves mechanical safety, lightweight, and smaller size. This manipulator uses the virtual sphere principle. Only two motors manipulate this robot (having 6DOF): one for drive, and the other for transmission, minimizing the risk of wrong movement of the manipulator. This manipulator can be driven in an MRI gantry, but the MRI images are distorted due to the presence of the manipulator. We also developed the algorithm that corrects MRI image distortion, using primary liner correction method. [Experimental results & Discussion] We confirmed the movement of the manipulator in MRI gantry (magnetic field of 0.5T). The accuracy of the movement was within 0.5mm for each axis. Backlashes were within 2mm, which is not so small. However since we plan to use “one-way movement”, backlash will no longer be a problem. The correction reduced MRI image distortions in major parts (drifts in coordinate were within 2mm). In some region, conversely, it increased to 4mm over. Therefore we have to improve algorithm further. This research is partly supported by JSPS-RFTF96P00801 program, Grant-in-Aided for Encouragement of Young Scientists. REFERENCE [1] K. Masamune, et al., “Development of an MRI-Compatible Manipulator for Stereotactic Neurosurgery”, J. of Image Guided Surgery, pp242-248, 1995. [2] K. Masamune, et al., “A newly Developed Stereotactic Robot with Detachable Drive for Neurosurgery”, MICCAI’98, pp.215-222, 1998. Main Mechanical Component